In situ coupling of Co_0.85Se and N-doped carbon via one-step selenization of metal-organic frameworks as a trifunctional catalyst for overall water splitting and Zn-air batteries

Developing efficient noble metal-free multifunctional electrocatalysts is highly effective to dramatically reduce the overall cost of electrochemical devices. In this work, we demonstrate for the first time a facile strategy for in situ coupling of ultrafine Co_0.85Se nanocrystals and N-doped carbon (Co_0.85Se@NC) by directly selenizing zeolitic imidazolate framework-67 (ZIF-67) polyhedra. Benefiting from the synergistic effect of the coupling between Co_0.85Se and NC, the Co-N-C structure, and the porous conductive carbon network, Co_0.85Se@NC affords excellent oxygen evolution reaction (OER) performance with a small overpotential, remarkable stability, and high faradaic efficiency. Furthermore, Co_0.85Se@NC can also efficiently catalyze hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), and we therefore investigated its applications as a trifunctional electrocatalyst for overall water splitting and Zn-air batteries. When used as both the anode and cathode for overall water splitting, a low cell voltage of 1.76 V is sufficient to reach the current density of 10 mA cm⁻²; the obtained Zn-air batteries exhibit a very low discharge-charge voltage gap (0.80 V at 10 mA cm⁻²) and long cycle life (up to 180 cycles). These results not only demonstrate a facile strategy for the synthesis of affordable Co_0.85Se@NC but also present its huge potential as a trifunctional electrocatalyst for clean energy systems.